The present invention relates to expansible fixing plugs composed of a plastic material.
More particularly, it relates to an expansible fixing plug which has a slot extending over a part of its length and a longitudinal channel provided for insertion of a fixing screw or the like.
Expansible fixing plugs of the above mentioned general type are known in the art. One of such plugs is disclosed for example in the German patent document DE-PS 10 97 117. This document discloses a cylindrical expansible fixing plug provided with a slit extending over a part of its length, and a rear end provided with a longitudinal bore for insertion of a fixing screw. The front portion of the longitudinal bore is cylindrical and has a diameter corresponding approximately to an external diameter of the fixing screw. Adjoining the cylindrical portion, there is a conical taper which terminates in the slit of the fixing plug and has the shape of the clef in the leading end region. The conical taper of the longitudinal bore of the fixing plug causes a circular-section narrowing which presents a high insertion resistance as the fixing screw is screwed in. Although the expansible segments of the fixing plug formed by the longitudinal slot are yieldable at right angles to the plane of the slot to reduce the insertion resistance, in the plane of the slot the thread of the fixing screw must nevertheless become cut fully into the material of the fixing plug. Since the fixing plug cannot extend in the plane of the slot, this increased insertion resistance is not converted into a corresponding expansion force. Because of the increased insertion resistance, it is possible, particularly in the case of drilled holes that are too big, for the fixing plug to turn with the fixing screw as it is screwed in, despite anti-rotation ribs arranged on the outer circumference of the plug.
The German patent document DE 41 17 503 A1 discloses an improved fixing plug in which it is proposed to narrow the cylindrical portion of the cylindrical bore at right angles to the plane of the slot to the width of the slot. The diameter of the cylindrical portion and the plane of the slot is approximately retained in the region of the narrowing. Therefore, a narrowing of the elliptical cross-section is produced, so that insertion resistance is reduced. However, the guidance of the screw is adversely affected as it is screwed into the fixing plug. As a result, the screw may therefore run off course in the fixing plug, and it becomes impossible to anchor the fixing plug properly.